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PubMed2005

Signal evolution in prey recognition systems.

In this paper a graphical model first developed in the context of kin recognition is adapted to the study of signalling in predator-prey systems. Antipredation strategies are envisioned as points along a signal-to-noise (S/N) axis, with concealing (low S/N) and conspicuous (high S/N) strategies being placed at opposite sides of this axis. Optimal prey recognition systems should find a trade-off between acceptance errors (going after a background cue as if it were a prey) and rejection errors (not going after a prey as if it were background noise). The model also predicts the types of cues the predator should use in opposite sides of the S/N axis.

Animals↗
PubMed2005

Impaling in true shrikes (Laniidae): a behavioral and ontogenetic perspective.

The impaling of prey is a behavioral trait restricted to the true shrikes (Laniidae). Here, we suggest the ontogeny of this behavior. We believe impaling originated from wedging behavior that occurs among several other groups of birds, including corvids. Accidental impaling during wedging was likely the behavioral precursor of purposeful impaling. Fidelity to impaling sites lead to the creation of caches, which were eventually used by females for male evaluation. Caching allowed males to increase their fitness by using the caches as a display to attract potential mates. Further, caching is used by shrikes to demarcate territories, store food for inclement weather or periods of stress in the breeding cycle, divide labor between the breeding pair, and for "aging" while deterrent chemicals in prey decompose.

Animals↗
PubMed2005

Social learning in noncolonial insects?

Social-information use has generated great interest lately and has been shown to have important implications for the ecology and evolution of species. Learning about predators or predation risk from others may provide low-cost life-saving information and would be expected to have adaptive payoffs in any species where conspecifics are observable and behave differently under predation risk. Yet, social learning and social-information use in general have been largely restricted to vertebrates. Here, we show that crickets adapt their predator-avoidance behavior after having observed the behavior of knowledgeable others and maintain these behavioral changes lastingly after demonstrators are gone. These results point toward social learning, a contingency never shown before in noncolonial insects. We show that these long-lasting changes cannot instead be attributed to long re-emergence times, long-lasting effects of alarm pheromones, or residual odor cues. Our findings imply that social learning is likely much more phylogenetically widespread than currently acknowledged and that reliance on social information is determined by ecological rather than taxonomic constrains, and they question the generally held assumption that social learning is restricted to large-brained animals assumed to possess superior cognitive abilities.

Analysis of Variance↗
PubMed2004

Natural selection on unpalatable species imposed by state-dependent foraging behaviour.

Müllerian mimicry is typically thought to arise as a consequence of defended prey species adopting a similar way of signalling their unprofitability, thereby reducing the costs of predator education. Here we consider subsequent selection on the morphology of prey species, in the potentially lengthy period of time when predators are generally aware of the noxious qualities of their prey (and so no further learning is involved). Using a pair of stochastic dynamic programming equations which describe both the toxin burdens of a predator and its energy level, we identified the optimal state-dependent rules that maximize a predator's long-term survivorship, and examined the implications of this behaviour for the evolution of prey morphologies. When palatable prey are in short supply then those prey species which contain relatively low doses of toxins become profitable to consume by hungry predators. Under these conditions, a weakly defended prey could gain selective advantage in the post educational period by resembling a prey species which contained a higher dose of the same or different toxins, although the precise nature of the ecological relationship between model and mimic could either be mutualistic or parasitic depending on how mimic density increases when favoured by selection. Our work formally demonstrates that one does not always need to invoke educational effects to explain why two or more unpalatable species have evolved a similar appearance, or to explain why mimetic similarity among distasteful species is maintained over time. When two species contain high levels of different toxins then they may gain mutual advantage by resembling one another, not only by educating the predator as to their common unprofitability (classical Müllerian mimicry), but also by increasing predator uncertainty as to the specific kind of toxin a prey item contains.

Adaptation, Physiological↗
PubMed2005

Reinforcement learning for a stochastic automaton modelling predation in stationary model-mimic environments.

In this paper we propose a mathematical learning model for the feeding behaviour of a specialist predator operating in a random environment occupied by two types of prey, palatable mimics and unpalatable models, and a generalist predator with additional alternative prey at its disposal. A well known linear reinforcement learning algorithm and its special cases are considered for updating the probabilities of the two actions, eat prey or ignore prey. Each action elicits a probabilistic response from the environment that can be favorable or unfavourable. To assess the performance of the predator a payoff function is constructed that captures the energetic benefit from consuming acceptable prey, the energetic cost from consuming unacceptable prey, and lost benefit from ignoring acceptable prey. Conditions for an improving predator payoff are also explicitly formulated.

Algorithms↗
PubMed2005

Molecular phylogeny of selected predaceous leeches with reference to the evolution of body size and terrestrialism.

The phylogenetic relationships of erpobdellid leeches collected throughout Europe were investigated using newly obtained mitochondrial cytochrome c oxidase subunit I (CO-I) gene sequence data from 10 taxa. Monophyly of the five European Erpobdella species (sub-family Erpobdellinae) was supported, but a newly discovered leech, E. wuttkei Kutschera, 2004 (the smallest member of its genus, discovered in an aquarium) was only distantly related to this clade. Three members of the semiaquatic Trochetinae were included in this study. The largest European leech species discovered so far, Trocheta haskonis Grosser, 2000, was found to be a terrestrial predator that feeds on earthworms. The rare species T. haskonis is the sister taxon of T. bykowskii Gedroyc, 1913, a well-known amphibious leech. Based on a comparison of body sizes and a phylogenetic tree the evolution of terrestrialism in the family Erpobdellidae is discussed.

Aging↗
PubMed2003

Intrinsic qualities of primate bones as predictors of skeletal element representation in modern and fossil carnivore feeding assemblages.

Plio-Pleistocene faunal assemblages from Swartkrans Cave (South Africa) preserve large numbers of primate remains. Brain, C.K., 1981. The Hunters or the Hunted? An Introduction to African Cave Taphonomy. University of Chicago Press, Chicago suggested that these primate subassemblages might have resulted from a focus by carnivores on primate predation and bone accumulation. Brain's hypothesis prompted us to investigate, in a previous study, this taphonomic issue as it relates to density-mediated destruction of primate bones (J. Archaeol. Sci. 29, 2002, 883). Here we extend our investigation of Brain's hypothesis by examining additional intrinsic qualities of baboon bones and their role as mediators of skeletal element representation in carnivore-created assemblages. Using three modern adult baboon skeletons, we collected data on four intrinsic bone qualities (bulk bone mineral density, maximum length, volume, and cross-sectional area) for approximately 81 bones per baboon skeleton. We investigated the relationship between these intrinsic bone qualities and a measure of skeletal part representation (the percentage minimum animal unit) for baboon bones in carnivore refuse and scat assemblages. Refuse assemblages consist of baboon bones not ingested during ten separate experimental feeding episodes in which individual baboon carcasses were fed to individual captive leopards and a spotted hyena. Scat assemblages consist of those baboon bones recovered in carnivore regurgitations and feces resulting from the feeding episodes. In refuse assemblages, volume (i.e., size) was consistently the best predictor of element representation, while cross-sectional area was the poorest predictor in the leopard refuse assemblage and bulk bone mineral density (i.e., a measure of the proportion of cortical to trabecular bone) was the poorest predictor in the hyena refuse assemblage. In light of previous documentation of carnivore-induced density-mediated destruction to bone assemblages, we interpret the current findings as suggestive of the secondary importance of bulk bone mineral density to other intrinsic qualities of skeletal elements (e.g., size, maximum dimension, and average cross-sectional area). It is only when skeletal elements are too large for consumption (e.g., many long bones) that they are fragmented following intra-element patterns of density-mediated carnivore destruction. There appears to be a size threshold beneath which bulk bone mineral density contributes little to mediating carnivore destruction of carcasses. Thus, depending on body size of the predator, body size of the prey, and specific size of the element, bulk bone mineral density may play little or no role of primary importance in mediating the destruction of skeletal elements. We compare patterns in modern comparative assemblages to patterns in primate fossil assemblages from Swartkrans. One of the fossil assemblages, Swartkrans Member 1, Hanging Remnant, most closely approximates a hyena (possibly refuse) assemblage pattern, while the Swartkrans Member 2 assemblage most closely approximates a leopard (possibly scat) assemblage pattern. The Swartkrans Member 1, Lower Bank, assemblage does not closely approximate any of our modern comparative assemblage patterns.

Animals↗
PubMed1998

Benzodiazepine and serotonergic modulation of antipredator and conspecific defense.

The mammalian defense repertory comprises an array of individual behaviors that are extraordinarily sensitive to relevant features of the threat stimulus and the situation in which it occurs. In parallel with increasing awareness of the specificity and complexity of defensive behaviors and of their potential relevance to psychopathologies (e.g. anxiety, panic, and depression) is an escalating use of natural threat stimuli such as attacking conspecifics or predators in paradigms aimed at evaluating drug effects on defense. A review of the literature on benzodiazepine (BZ) and serotonin (5-HT) effects on conspecific and antipredator defense, including defensive analgesia, indicates that both types of stimuli elicit a wide array of relevant defensive behaviors. These studies suggest specificity of drug effects on particular behaviors, rather than a general alteration of all aspects of defense. However, stimulus variability and possible confounding of effects are a considerable problem with conspecific defense paradigms, while antipredator paradigms utilizing human experimenters as the predator may be difficult to use with the domesticated laboratory animal subjects. In addition, sensitivity to the organization of defensive behaviors and to differences between species in defense patterns is necessary to adequate interpretation of results. Nonetheless, these paradigms have permitted major advancements in analysis of the behavioral defense systems and their sensitive use in drug studies will greatly facilitate an understanding of the physiology of defense.

Agonistic Behavior↗
PubMed2000

[Morphofunctional analysis and trophic adaptations: the case of bill apparatus of Old World flycatchers].

A morphofunctional analysis of the bill apparatus was conducted on some African forest flycatchers (Muscicapidae, Platysteiridae, Monarchidae) in relation to detailed eco-ethological data available on these species. The aim was to evaluate relationships between anatomical structures and habitat constraints and also identify the most pertinent trophic adaptations. If forest Muscicapidae have essentially conserved the generalized passerine structures and occupy open-habitat niches in the forest, Platysteiridae and Monarchidae have adapted to forest conditions and show a key-adaptation based on specific changes in the structure of the bill apparatus in response to particular light patterns and habitat clogginess, constraints that require speed and precision for the capture of prey and protection of the skull against collisions.

Adaptation, Physiological↗
PubMed2002

Significance of predation by protists in aquatic microbial food webs.

Predation in aquatic microbial food webs is dominated by phagotrophic protists, yet these microorganisms are still understudied compared to bacteria and phytoplankton. In pelagic ecosystems, predaceous protists are ubiquitous, range in size from 2 gm flagellates to > 100 microm ciliates and dinoflagellates, and exhibit a wide array of feeding strategies. Their trophic states run the gamut from strictly phagotrophic, to mixotrophic: partly autotrophic and partly phagotrophic, to primarily autotrophic but capable of phagotrophy. Protists are a major source of mortality for both heterotrophic and autotrophic bacteria. They compete with herbivorous meso- and macro-zooplankton for all size classes of phytoplankton. Protist grazing may affect the rate of organic sinking flux from the euphotic zone. Protist excretions are an important source of remineralized nutrients, and of colloidal and dissolved trace metals such as iron, in aquatic systems. Work on predation by protists is being facilitated by methodological advances, e.g., molecular genetic analysis of protistan diversity and application of flow cytometry to study population growth and feeding rates. Examples of new research areas are studies of impact of protistan predation on the community structure of prey assemblages and of chemical communication between predator and prey in microbial food webs.

Animals↗
PubMedDate not supplied

Stunning whales.

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Animals↗
PubMed2005

Insect behaviour: migratory bands give crickets protection.

Mormon crickets and juvenile locusts form huge migratory bands--millions of individuals march in unison across the landscape and devastate vast agricultural areas, but little is known about why these bands form. Here we use radiotelemetry to show that band membership benefits these insects by greatly reducing the probability that they will become victims of predators. It is likely that migratory banding has evolved because it gives substantial protection to individuals within the group.

Animal Migration↗
PubMed2001

Maternal effects and the evolution of aposematic signals.

Aposematic signals that warn predators of the noxious qualities of prey gain their greatest selective advantage when predators have already experienced similar signals. Existing theory explains how such signals can spread through selective advantage after they are present at some critical frequency, but is unclear about how warning signals can be selectively advantageous when the trait is initially rare (i.e., when it first arises through mutation) and predators are naive. When aposematism is controlled by a maternal effect gene, the difficulty of initial rarity may be overcome. Unlike a zygotically expressed gene, a maternally expressed aposematism gene will be hidden from selection because it is not phenotypically expressed in the first individual with the mutation. Furthermore, the first individual carrying the new mutation will produce an entire family of aposematic offspring, thereby providing an immediate fitness advantage to this gene.

Animals↗
PubMed2004

New insights into chimpanzees, tools, and termites from the Congo Basin.

The tool-using behaviors of wild chimpanzees comprise the most impressive assemblages and flexible repertoires of nonhuman material culture. We expand knowledge of the breadth and complexity of tool use in this species by providing the first descriptions of the form and function of two distinct tool sets used by chimpanzees in preying upon termites within the forests of the Goualougo Triangle, Republic of Congo. Further, we report the first application of remote video monitoring technology to record wild chimpanzee tool-using behavior. Based on tool assemblages recovered at termite nests, we hypothesized that chimpanzees were regularly visiting two forms of termite nests and using specific tools to extract termite prey depending on the structure of the nest. Six months of continuous remote video monitoring at six termite nests confirmed that chimpanzees use a tool set to puncture and fish at subterranean termite nests and another tool set to perforate and fish at epigeal (aboveground) nests. Our findings of strict adherence to tool forms at different nest types, tool material selectivity, repeated visits to nests with reusable wood tool assemblages, and differences in material culture between communities have broad implications for our understanding of the ecological and cultural factors that shape hominoid tool use.

Animals↗
PubMed2006

Efficiency evaluation of two competing foraging modes under different conditions.

Various foraging modes are employed by predators in nature, ranging from ambush to active predation. Although the foraging mode may be limited by physiological constraints, other factors, such as prey behavior and distribution, may come into play. Using a simulation model, we tested to what extent the relative success of an ambush and an active predator changes as a function of the relative velocity and movement directionality of prey and active predator. In accordance with previous studies, we found that when both active predator and prey use nondirectional movement, the active mode is advantageous. However, as movement becomes more directional, this advantage diminishes gradually to 0. Previous theoretical studies assumed that animal movement is nondirectional; however, recent field observations show that in fact animal movement usually has some component of directionality. We therefore suggest that our simulation is a better predictor of encounter rates than previous studies. Furthermore, we show that as long as the active predator cannot move faster than its prey, it has little or no advantage over the ambush predator. However, as the active predator's velocity increases, its advantage increases sharply.

Animals↗